During intense spring and early summer storms, substantial volumes of dust from east Asian desert regions are lofted over the continent and transported by prevailing winds across the Pacific Ocean. The phenomenon has wide reaching effects including long range nutrient and sediment transport as well as radiative forcing. Mauna Loa Observatory (MLO) is an atmospheric baseline station in Hawaii at an altitude of 3397-m.a.s.l.. MLO’s CCD Camera Lidar (CLidar) has fine near-ground altitude resolution, which makes it a useful system for Asian dust detection, especially at high altitude sites such as MLO. A 20-Watt, 532-nm Nd:YAG laser was vertically transmitted into the atmosphere above MLO. The side-scatter from atmospheric constituents, such as clouds, aerosols, and air molecules was detected by a wide-angle CCD camera situated 139-m from the laser. The obtained signal was range-normalized using a molecular scattering model and corrected for transmission with a column-averaged aerosol phase function derived from MLO-based AERONET photometer measurements. In several of the resulting aerosol extinction profiles, notable aerosol layers were observed near altitude ranges in which Asian dust is typically transported by prevailing winds. Corresponding relative humidity measurements made by nearby radiosondes were examined to differentiate aerosol scattering from cloud scattering. To further examine layers exhibiting both aerosol extinction peaks and relative humidity levels below that of tenuous ice clouds, back trajectories were conducted using NOAA’s Hybrid Single Particle Lagrangian Integrated Trajectory model. Several layers from 2008 and 2009 were traced back to East Asian deserts.
NASA’s Goddard Space Flight Center (GSFC) transported two lidar instruments to the NOAA facility at the Mauna Loa Observatory (MLO) on the Big Island of Hawaii, to participate in an official, extended validation campaign. This site is situated 11,141 ft. above sea level on the side of the mountain. The observatory has been making atmospheric measurements regularly since the 1950’s, and has hosted the GSFC Stratospheric Ozone (STROZ) Lidar and the GSFC Aerosol and Temperature (AT) Lidar on several occasions, most recently between November, 2012 and November, 2015. The purpose of this extended deployment was to participate in Network for the Detection of Atmospheric Composition Change (NDACC) Validation campaigns with the JPL Stratospheric Ozone Lidar and the NOAA Temperature, Aerosol and Water Vapor instruments as part of the routine NDACC Validation Protocol.
A wide-angle CCD camera based bistatic lidar (CLidar) is used to monitor aerosol profiles in the atmosphere of The Bahamas. A 2-Watt CW laser beam ranging from ground to zenith is captured in a single image by a camera fitted with a fisheye lens which is placed at a different location from the laser. Scattering altitude is determined simply from the geometry of the CLidar in contrast to monostatic lidar which requires expensive electronics to measure the time of flight of the returned signal. Each image contains both molecular and aerosol single angle scattering. A cloud free image is used to normalize the signal intensity to a model of molecular scattering at a region free of aerosol layer. Then molecular portion is subtracted to retrieve aerosol side scattering. An aerosol phase function was assumed to convert side scatter to aerosol extinction. Corrections due to transmission effects are then iteratively calculated until convergence is reached. Aerosol extinction drops off sharply above 1 km indicating the planetary boundary level which agrees well with the relative humidity measurements obtained from the radiosonde data of Nassau airport observation. Additionally, aerosols originated from the smoke of a charcoal grill operating near experimental site were efficiently detected near ground levels. Aerosol extinction at 20 m above sea level is 0.085 km-1 during grilling compared to 0.03 km-1 during no grilling. Excellent altitude resolution of the CLidar at the ground levels allows its use for in-situ environmental characterization without the overlap effects faced when using traditional lidar.
A bistatic CCD camera lidar (CLidar) was used at the National Oceanic and Atmospheric Administration’s Mauna Loa
Observatory (MLO) to map aerosol light scattering. Laser light from a 532 nm, Nd:YAG laser was vertically transmitted
into the atmosphere and the scatter off clouds, aerosols and air molecules was detected using a CCD camera with wide
angle optics and a laser line filter. The intensity of each CCD camera pixel imaging the beam was normalized to a
molecular scattering model in an aerosol free region for subtraction of molecular scattering. Aerosol extinction was
derived using a column average aerosol phase function derived from AERONET sun photometer measurements at MLO.
The CLidar design allows measurements of aerosol scattering all the way to the ground without an overlap correction.
MLO, at 3397 m.a.s.l., typically receives free tropospheric air. During spring months, prevailing winds can occasionally
transport dust from Asian sources with high dust activity over MLO. Aerosol scattering measurements were taken by the
CLidar during spring months at MLO and revealed extinction peaks at mid-range altitudes. Back trajectories of air
parcels from MLO at the altitudes of these peaks were conducted using NOAA’s Hybrid Single Particle Lagrangian
Integrated Trajectory (HYSPLIT) model and it was found that they passed over regions of Eastern Asia known as
sources of high dust activity. Relative humidity data from radiosondes and the NOAA stratospheric lidar’s water vapor
channel were examined to differentiate aerosol scattering from tenuous cloud scattering. This paper presents aerosol
extinction data with observations of Asian dust as measured by the CLidar during spring months at MLO.
An innovative, ground-based bistatic lidar receiver to measure aerosol scattering in the atmospheric boundary layer has been developed and tested for proof-of-concept. The raster-mirror designs have greater than two orders of magnitude light gathering capability, and higher altitude resolution than the design used in Barnes et. al., thus allowing the use of lower power eye safe lasers. The design is based on dividing the wide 100° vertical field of view into several sectors, using 1-D rastering of mirrors and parallel imaging of the laser light scattered from each sector onto one CCD while employing a single narrow angle-of-view objective. The system is applicable for simultaneous measurements of several laser beams to obtain spectral, spatial, and temporal information about the atmosphere. Using an off-axis parabolic mirror objective eliminates chromatic aberrations, making the system employable in a broad spectral range from IR to UV. The advantages of the proposed technology are: the ability to control the dynamic range of the registered signal, the superior height resolution of 14 mm/pixel at the ground level, and 175m/pixel at 20km altitude, low cost, and simplicity. The bistatic CLidar receiver will include automatic system feedback and self-calibration. The system will be developed to accommodate daytime operational conditions.
A CCD based bistatic lidar (CLidar) system has been developed and constructed to measure scattering in the atmospheric boundary layer. The system used is based on a CCD camera, wide-angle optics and laser. Measuring near the ground with the standard monostatic lidar method is difficult due to the huge change in signal strength with altitude and the incomplete overlap between the laser and the telescope. High spatial (altitude) resolution is also desired near the ground for comparison with in-situ aerosol instruments. Imaging a vertical laser beam from the side with a CCD camera and wide-angle field of view optics overcomes both of these problems. While the molecular signal changes many orders of magnitude in the standard method, it only changes about one order with the CLidar method. In addition, the CLidar resolution near the ground is less than a meter. For perpendicular polarization, the molecular signal is nearly constant all the way to the ground. Other advantages of the CLidar method include low cost and simplicity. The signal is integrated on the CCD rather than with specialized electronics. With the bistatic CLidar method the scattering angle changes with altitude. The variation of scattering intensity with the scattering angle will be influenced by the aerosol size distribution and thus could help provide information on aerosol parameters of interest in
the boundary layer.
Water vapor measurements have been added to the aerosol/temperature lidar operated by the NOAA/Climate Monitoring and Diagnostics Laboratory at Mauna Loa Observatory (MLO). The 532 nm light from an Nd:YAG laser is used and two channels measure the raman shifted light at 607 nm (nitrogen) and 660 nm (water vapor). The receiver is a 74 cm diameter parabolic mirror with the two detectors at the prime focus. An interference filter and two high pass filters achieve a rejection of the 532 nm light of about 1E9, which is needed for measurements of water in the upper troposphere where the water mixing ration can be a few parts per million. Radiosonde flights from the observatory were used for both the calibration constant and the low altitude overlap corrections. The sonde flights used both Vaiasala humidity sensors and chilled mirror hygrometers. The Vaiasala sensors were accurate to about 11 km (-50°C). The chilled mirror hygrometer detection limit is determined by the temperature depression attainable by the cooler. The lidar system has been used for validation of the Atmospheric Infrared Sounder (AIRS) on the NASA/Aqua satellite launched in May, 2002.
A CCD based bistatic lidar (CLidar) system has been developed and constructed to measure scattering in the atmospheric boundary layer. The system used is based on a CCD camera, wide-angle optics and laser. Measuring near the ground with the standard monostatic lidar method is difficult due to the huge change in signal strength with altitude and the incomplete overlap between the laser and the telescope. High spatial (altitude) resolution is also desired near the ground for comparison with in-situ aerosol instruments. Imaging a vertical laser beam from the side with a CCD camera and wide-angle field of view optics overcomes both of these problems. While the molecular signal changes many orders of magnitude in the standard method, it only changes about one order with the CLidar method. In addition, the CLidar resolution near the ground is less than a meter. For perpendicular polarization, the molecular signal is nearly constant all the way to the ground. Other advantages of the CLidar method include low cost and simplicity. The signal is integrated on the CCD rather than with specialized electronics. With the bistatic CLidar method the scattering angle changes with altitude. The variation of scattering intensity with the scattering angle will be influenced by the aerosol size distribution and thus could help provide information on aerosol parameters of interest in the boundary layer.
A CCD based bistatic lidar (CLidar) system has been developed and constructed to measure scattering in the atmospheric boundary layer. The system used is based on a CCD camera, wide-angle optics and laser. Measuring near the ground with the standard monostatic lidar method is difficult due to the huge change in signal strength with altitude and the incomplete overlap between the laser and the telescope. High spatial (altitude) resolution is also desired near the ground for comparison with in-situ aerosol instruments. Imaging a vertical laser beam from the side with a CCD camera and wide-angle field of view optics overcomes both of these problems. While the molecular signal changes many orders of magnitude in the standard method, it only changes about one order with the CLidar method. In addition, the CLidar resolution near the ground is less than a meter. For perpendicular polarization, the molecular signal is nearly constant all the way to the ground. Other advantages of the CLidar method include low cost and simplicity. The signal is integrated on the CCD rather than with specialized electronics. With the bistatic CLidar method the scattering angle changes with altitude. The variation of scattering intensity with the scattering angle will be influenced by the aerosol size distribution and thus could help provide information on aerosol parameters of interest in the boundary layer.
An incoherent (direct detection) Doppler lidar is developed that operates in the middle of the visible spectrum and measures wind and aerosol profiles during the day and night from the planetary boundary layer to the lower stratosphere. The primary challenge of making a lidar measurement in the visible spectrum during daylight hours is the strong presence of background light from the sun. To make a measurement of this type, the laser line must be isolated spectrally to the greatest extent possible. This has been accomplished through the use of a multiple étalon Fabry-Pérot interferometer in combination with a narrow-band filter. The incoherent technique and system are a modified version of the Fabry-Pérot interlerometer and image-plane detector technology developed for an earlier Doppler lidar developed at the University of Michigan and for the High-Resolution Doppler Imager (HRDI) now flying on the Upper Atmosphere Research Satellite. The incoherent Doppler analysis is discussed and sample measurements are shown. Winds are measured in the boundary layer with 100-m vertical resolution and 5-mm temporal resolution with 1 to 3 m s-1 accuracy.
The University of Michigan's Space Physics Research Laboratory has constructed a mobile high-spectral-resolution Doppler lidar capable of measuring wind and aerosol loading profiles in the troposphere and lower stratosphere. The system uses a 3-W pulsed frequency-doubled Nd:YAG laser operating at 532 nm as the active source. Backscattered signal is collected by a 44.4-cm-diameter Newtonian telescope. A two axis mirror scanning system allows the instrument to achieve full sky coverage. A pair of Fabry-Perot interferometers in combination with a narrowband (0.1nm) interference filter are used to filter daylight background and provide a high spectral resolving element to measure the Doppler shift. In addition, the aerosol and molecular scattered components of the signal can be separated, giving a measure of the relative aerosol loading. Measurements have been made day and night in the boundary layer with vertical resolution of 100 m and a temporal resolution of approximately 5 minutes. Accuracy of the wind velocity is on the order of 1 to 2 m/s in the boundary layer.
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